Magnetic amplifiers



March 26, 1963 R. M. HUBBARD MAGNETIC AMPLIFIERS 2 Sheets-Sheet 1 Original Filed July 22, 1959 JNVENToR. @055er M Hagi/WD March 26, 1963 R. M. HUBBARD MAGNETIC AMPLIFIERS Original Filed July 22, 1959 2 Sheets-Sheet 2 Unite rates z cintas. (ci. S23-sa) This invention relates to magnetic amplifiers, and more particularly, to new and improved magnetic amplifiers of the selfasaturating type.

' The subject application is a continuatoin application of patent application Serial No. 828,750, filed July 22, 1959, now abandoned, and entitled Magnetic Amplifiers, and the subject application is related to patent application Serial No. 828,783, filed July 22, H959, and entitled Time Delay Circuits, and is related to patent application Serial 828,749, filed July 22, i959, and entitled Full-Wave Magnetic Amplifiers (now United States Patent No. 3,002,145).

Conventional magnetic ampliers of the self-saturating type are characterized by having a load circuit in which the load is in series circuit relationship with .the load winding, the self-saturating rectifier, and a source of alternating voltage. Although this type of prior art magnetic amplifier has relatively high `efiiciency, it has several limita-tions. For instance, although the average voltage across lthe gate or load winding is proportional to the magnitude of the input control signal .to the magnetic amplifier, the voltage appearing across the load is directly Vaffected by any changes in the magnitude of the supply voltage to the magnetic amplifier since, as hereinbefore mentioned, the source of supply volta-ge is in series circuit relationship with the load winding and the load.

In addition, in the conventional self-saturating magnetic amplifier, such as Logans sel-saturating magnetic amplifier, the magnitude of the voltage across the load decreases with an increase in magnitude of the input control signal unless separate lbiasing means is provided. However, when separate biasing means is provided, any change in the magnitude of the biasing signal effects a change in the magnitude of the voltage across the load connected to the amplifier, thus effecting drift. If two of these conventional self-saturating amplifiers are connected in cascade to establish two stages, the second stage must also be provided with :separate biasing means in order for the output signal from the second stage to increase in magnitude with an increase in the magnitude of the input signal to the first stage. Here again the introduction of biasing means into the second stage causes the amplifier to drift.

A further disadvantage of conventional self-saturating magnetic amplifier circuitry is that when two full-wave stages are connected in cascade, they are normally conpled -by a power wasting forcing resistance to insure fast response in the second stage. Also, normally the highly peaked output voltage wave form of the first stage effects rectifier unblocking in the second stage unless some decoupling interstage filtering is utilized. This filtering, of course, lengthens the response time of the amplifier.

The most important defliciency of two half-wave conventional self-saturating magnetic amplifiers when connected in cascade is the gate circuit loading of the second stage during the second stage gating half-cycle. During this gating half-cycle the induced voltage effected in the Asecond stage control winding adds to the induced vol-tage in the first stage load winding to oppose the supply Voltage and thereby cause the first stage self-saturating rectifier to conduct when in reality it should be blocking. In other Words, if the first stage self-saturating rectifier fails to perform its function of blocking, the control circuit of the first stage offers a low impedance reected to the gate circuit of the second stage and therefore appreatuv i 3,883,334- Patented Mar. 26, 1963 ciable current flows to the second stage load before the gate winding of the second stage effects a saturation of its associated core, and thus the difference current to the load before and after saturation of this core is relatively small. Commonly a resistance is added in series with the second stage control Winding to alleviate, but never correct, this situation.

In a conventional full-wave self-saturating magnetic amplifier having series connected control windings, one of the cores of the magnetic amplifier is being reset while the other core of the magnetic amplifier is being gated. Such being the case a voltage is reflected back into the control circuit by the action of the core being gated, to thus effect a feedback action in which this reflected voltage effects the magnitude of the control signal being applied to the core being reset. This results in an increase in the response time of the magnetic amplifier.

An important limitation on the design of half-wave stages 4in cascade when utilizing conventional self-saturating magnetic amplifiers is imposed by the fact that the impedance presented by the control winding of the second stage must be small compared to the unsaturated impedance of the gate winding of the first stage in order -toobtain a good dynamic range for the magnetic amplifier stages. For instance, if the impedance presented by the control winding of the second stage is substantially equal to the unsaturated impedance of the gate winding of the first stage, there will only be a two-.to-one change in the magnitude of the voltage appearing across the control winding of the second stage in going from the nonsaturated -to the saturated state in the first stage. This, of course, is not good dynamic range.

A conventional self-saturating magnetic amplifier having positive feedback effects an output voltage with no control signal input to the amplifier. On the other hand, a conventional self-saturating magnetic amplifier having a large amount of negative feedback effects a cut-ofi voltage across the load with no control signal input. Oftentimes, it is desirable to attain just the opposite effect, that is with positive feedback to have the output voltage of the magnetic amplifier at cut-off with no control signal input and with negative feedback to have the output voltage of the magnetic amplifier at the saturated value with no control signal input.

Therefore, an object of this invention is Ito provide for so coupling aload to the gate circuit of a magnetic amplifier that the voltage across the load is substantially directly proportional and substantially equal to the gate voltage -to thus effect an 'efficient transfer of the gate voltage to the load in a manner that the voltage across the load is substantially independent of the magnitude of the supply voltage to the magnetic amplifier, to thereby `render the magnitude of the load voltage proportional only to the control signal applied to the magnetic amplifier.

Another object of this invention is to provide for rendering-the load voltage of a magnetic amplifier substantially directly proportional to its input control signal, that is, an increase in the magnitude of the control effects an increase in the magnitude of the load voltage, without the aid of biasing means, to thereby eliminate the undesired effect of biasing which changes the magnitude of the load voltage in accordance with the magnitude of the biasing signal.

A further object of this invention is to provide for eliminating biasing means for the second stage of a twostage magnetic amplifier, to thereby render the magnitude of the load voltage of the second stage independent of any such biasing means.

Still another object of this invention is `to provide for increasing the signal transfer efhciency between the first and second stage of a two-stage magnetic amplifier, by connecting the control circuit of the second stage in parallel circuit relationship with the gate circuit of the first stage, thereby eliminating the need for the conventional coupling.

A still further object of this invention is to provide for substantially eliminating loading of the gate circuit of the second stage during its gating half-cycle by blocking the ow of current through the reset Winding of the second stage during this gating half-cycle.

Another object of this invention is to provide for obtaining half-cycle response in the second stage of a fullwave two-stage magnetic amplifier, by providing complete isolation between the reset windings of the second stage.

A further object of this invention is to provide for simplifying the design problems in those magnetic amplifiers exhibiting half-cycle response in the second stage by eliminating the requirement that the impedance of the second stage control windings be low compared to the unsaturated impedance of the firs-t stage gate winding.

Still another object of this invention is to provide a positive feedback action in a magnetic amplifier that also etlects a biasing effect so that with no control signal input to the magnetic amplifier the output voltage of the magnetic amplifier can be at cut-olf.

Another object of this invention is to provide a negative feedback action in a magnetic amplilier that also efects a biasing effect so that with no control signal input to the magnetic amplifier the output voltage of the magnetic amplifier can remain at the saturated value.

Other objects of this invention will become apparent from the following description when taken in coniunction with the accompanying drawings in which:

FIG. l is a schematic diagram of a single-stage halfwave magnetic amplifier illustrating one embodiment of this invention;

FIG. 2 is a schematic diagram of two half-wave magnetic amplifiers connected in cascade illustrating another embodiment of this invention;

FlG. 3 is a schematic diagram of a two-stage full-wave magnetic amplier, having a non-reversible polarity input control signal, illustrating a further embodiment of this invention;

FIG. 4 is a schematic diagram of a two-stage half-wave magnetic amplier, having a dierential input control signal, illustrating still another embodiment of this invention;

FIG. 5 is a schematic diagram of still another embodiment of this invention in which feedback is provided, and

FIGS. 6A and 6B are graphs illustrating the feedback action of a conventional self-saturating magnetic amplilier and the magnetic amplifier shown in FIG. 5, respectively.

Referring to FIG. l there is illustrated a single stage half-wave magnetic `amplifier 10 embodying teachings of this invention. In operation, the magnetic amplifier iti eliects a halt-Wave voltage across a load 12, the magnitude of which is only proportional to the magnitude of the output voltage of a control source 13 which is connected to control terminals 14 and 14. In practice, the control source can either effect a direct-current voltage or an alternating voltage, however, the polarity of the control voltage during the reset half-cycle must be as indicated in FIG. l. As shown, the magnetic amplifier 10 comprises a magnetic core member 16, a reset winding 18 and a gate winding 29 disposed in inductive relationship with the magnetic core member 16.

In accordance with this invention, a parallel circuit Z2 is connected in series circuit relationship with a current source 24, one branch of the parallel circuit 22 including the load 12 and a rectifier 26 and the other branch of the parallel circuit 22 including the gate winding Ztl and a rectifier 2S. In this instance, the current source Z4 comprises a current-limiting resistor 3l) and supply terminals 32 and 32 to which is connected a source 33 of alternating voltage.

As illustrated, the rectiiiers 26 and 28 are so poled as to permit, only during alternate half-cycles of the voltage applied to the supply terminals 32 and 32', the flow of current through both branches of the parallel circuit 22. Specifically, current flows through both branches of the parallel circuit 22 only during those alternate halt-cycles of operation when the supply terminal 32 is at a positive polarity with respect to the supply terminal 32. During the other alternate half-cycles of operation when the supply terminal 32 is at a positive polarity with respect to the supply terminal 32', the rectiiers 26 and 28 block the llovv of current through both branches of the parallel circuit 22.

In order to reset the magnetic core member 16, during those half-cycles of operation when the supply terminal 32, is at a positive polarity with respect to the supply terminal 32', the reset winding 18 is connected to thel control terminals 14 and 14 through a current-limiting resistor M which in operation functions to cause the control circuit, including the reset winding 18 andthe resistor 3d, to offer a high impedance during that portion of the operation when the magnetic core member 16 is being gated.

In operation, the voltage across the load 12 is substantially directly proportional to and substantially equal to the gate voltage appearing across the gate winding 20, to thus effect an efficient transfer of the gate voltage to the load 12. Further, the magnitude of the voltage across the load 12 is substantially independent ot the magnitude of the supply voltage across the supply terminals 32 and 32. Therefore, the magnitude of the voltage across the load is proportional only to the magnitude of the input control voltage applied to the control terminal 1liand 14. It is also to be noted that an increase in the magnitude of the input control signal applied to the control terminais 14 and 14 ciiects an increase in the magnitude of the voltage appearing across the load 12. For instance, with the supply terminal 32 at a positive polarity with respect to the supply terminal 32, current flows from the supply terminal 32 through both branches of the parallel circuit 22 and the current-limiting resistor 30, to the supply terminal 32, to thereby eli'ect saturation of the magnetic core member 16. Until saturation, substantially all `of the voltage appearing across the supply terminals 32 and 32 appears across the gate winding 20 and the load 12. However, upon saturation of the magnetic core member 16, substantially all of the voltage across the supply terminals 32 and 32 then appears across the current-limiting resistor Siti. The proportion of the voltage appearing across the supply terminals 32 and 32 that appears across the load 12 is determined by the linxV level to which the magnetic core member 16 has been reset during the previous half-cycle by the action of the input control signal applied to the control terminals 14 and 14. Therefore, if the magnitude of the input control signal is increased, the magnetic core member 16y is reset to a lower flux level and magnetizing current must flow from the supply terminal 32 through the gate winding 2li for a longer portion of this half-cycle of operation and, therefore, the magnitude of the average voltage across the load 12 is increased.

Referring to FIG. 2 there is shown a two-stage halfwave magnetic amplifier 36 in which like components of FIGS. 1 and 2 have been given the same reference characters. In FIG. 2 the load i12 of FIG. l becomes a reset winding 3d in the second stage of the magnetic amplifier 136. Thus, the second stage of the magnetic amplifier 36 comprises the reset winding y38 which is disposed in inductive relationship with a magnetic core member4t), the rectifier 26, a gate winding 42 also disposed in inductive relationship with the magnetic core member 40, and circuit means 4f-l for effecting a gating of the magnetic core member 4t?. On the other hand, the first stage of the magnetic amplifier 36 includes the magnetic core member 16, the reset and gate windings 18 and 20, respectively, and the rectifier 28. Y

As illustrated, the circuit means 44 for effecting a gataosasa ing of the magnetic core member 40` includes a rectier 46, a load 48, and supply terminals 50 and S0 adapted to be connected to a source 51 of alternating voltage which is of the same frequency as the source 33 of alternating voltage connected to the supply terminals 32 and 32. In operation, the supply voltage applied to the supply terminals 56 and S0 mustbe so synchronized with the supply voltage applied to the supply terminals l32 and 32 that when the supply terminal 32 is at a positive polarity with respect to the supply terminal 32, the supply terminal Sil is at a positive polarity with respect to the supply terminal 50.

The operation of the apparatus and circuits of FIG. 2 will now be described. During the alternate half-cycles of operation when the supply terminal 32 is at a positive polarity with respect to the supply terminal i32 and the supply terminal 50 is at a positive polarity with respect to the supply terminal Si), current flows from the supply terminal 32 through a parallel circuit 52, one branch of which includes the gate winding 2t) and the rectifier `2S and the other branch of which includes the reset winding 38 and the` rectifier 26, and the currentlimiting resistor Cafl, to the supply terminal 32, to thereby gate the magnetic core member i6 and reset the magnetic core member 4i). During this same half-cycle of operation the rectifier 46 blocks the flow of current from the supply terminal 50 through the load 48 and the gate winding `42.

During the next half-cycle of operation, when the supply terminal 32 is at a positive polarity with respect to the supply terminal 32 and the supply terminal Sti is at a positive polarity with respect to the supply terminal 50', control current flows from the control terminal |14 through the current-limiting resistor 34 and the reset winding 13 to the control terminal 14', to thereby effect a resetting of the magnetic core member 16 in accordance with the magnitude of the input control signal applied to the control terminals 14 and 14'. Simultaneously, current flows from the supply terminal 50 through the gate winding 42, the rectifier 46 in the forward direction, and the load 4S, to the supply terminal 56, to thereby effect a voltage across the load 48 in accordance with the magnitude of the input control signal applied to the control terminals 14 and 14 during the previous reset half-cycle. During this same half-cycle of operation the rectifiers 26 and 23 block the flow of current through both branches of the parallel circuit '52.

It is to be noted that in the magnetic amplifier 36, loading of the gate circuit of the second stage is substantially eliminated since the rectifier 26 blocks the flow of current through the reset winding 38 during the halfcycle of operation when the magnetic core member 40 is being gated. Thus, in order to prevent loading of the gate circuit of the second stage of the magnetic amplifier 36, it is only necessary for the supply voltage applied to the supply terminals 32 and 32 to exceed the magnitude of the voltage induced across the reset winding 38 during the half-cycle of operation when the magnetic core member `4t) is being gated.

Referring to FlG. 3 there is illustrated a full-wave magnetic amplier 54 adapted to be controlled from a nonreversible polarity direct-current input control voltage and embodying further teachings of this invention. -Like components of FIGS. 2 and 3 have been given the same reference characters. Since the magnetic amplifier 54 of FIG. 3 comprises, in essence, two of the magnetic amplifiers 36 of FIG. 2 connected to effect full-wave alternating voltage across a load 56, the greater part of the lower portion of the magnetic amplifier 54 has been given the same reference characters as the upper portion of the magnetic amplifier 54, except that the reference characters applied to the lower portion of the magnetic amplifiers 54 have been given a prime.

In order to effect a flow of current through a parallel circuit 58, one branch of which includes the gate winding 20 and the rectifier 23' and the other branch of which includes the reset winding 38 and the rectifier 26', during the alternate half-cycles of operation that the rectifiers 26 and y28 of the parallel circuit 52 are preventing the fiow of current through the parallel circuit 52, the parallel circuit 58 is connected in series circuit relationship with the supply terminals 32 and 32' through a current-limiting resistor 6i).

-As shown, the reset winding 18 and the reset winding 18 are connected in series circuit relationship with the current-limiting resistor 34, the series circuit being connected to control terminal 62 and 62 which have connected thereto a source 63 of direct-current input control voltage of non-reversible polarity, to thus alternately effect a resetting of the magnetic core member 16 and 16 in accordance with the magnitude of the control voltage applied to the control terminals 62 and 62. On the other hand, in order to alternately effect a gating of magnetic core members 4u and 44)', the gate winding 42 is connected in series circuit relationship with the load S6 and with a rectifier -64 across supply terminals 66 and 66, whichV have connected thereto an alternating supply source 67 of the same frequency as the alternating supply source 33, the alternating voltage applied to the supply terminals 66 and 66 being synchronized with respect to the alternating voltage applied to the supply terminals 32 and 32 so that when supply terminal 32 is at a positive polarity with respect to the supply terminal 32, the supply terminal 66 is likewise at a positive polarity with respect to the supply terminal 66. rIn like manner, the gate winding 42 is connected in series circuit relationship with the load 56 and with a rectifier 6l; across the supply terminals 66 and 66.

The oper-ation of the magnetic amplifier 54 of FIG. 3 will now `be described. During alternate half-cycles of the supply voltage applied to the supply terminals 32 and 32' an-d to the supply terminals 66 and 66, the magnetic core members 16 and 40 are gated -and the magnetic core members 16 and 4t) are reset, to thus effect a flow of current from the supply terminal 66 through the load 56, the rectifier 68 in the forward direction, and the gate winding 42, to the supply terminal 66. During the other alternate half-cycles of `the supply voltage applied to the supply terminals 32 and 32' and to lthe supply terminals 66 and 66, the magnetic core members 16' and 40 are gated -and the magnetic core members 16 and 46 are reset, to thereby effect a iiow of current from the supply terminal 66 through the gate Winding 42, the rectifier 64 in the forward direction, and the load 56, to the supply terminal 66.

Specifically, during that half-cycle of operation when the supply terminal 32' is at a positive polarity with respect to the supply terminal 32 and the supply terminal 66 is at a positive polarity with respect to the supply terminal 66, current flows from the supply terminal 32' through both branches of the parallel circuit 52, and

the current-limiting resistor 30, to the supply terminal 32, to thereby effect a gating of the magnetic core mem- |ber 16 and a resetting of the magnetic core member 40. Simultaneously, ycontrol current flows from the control terminal 62 through the current-limiting resistor 34 and the reset windings 18 and 18 to the control terminal 62, to thus effect a resetting of the magnetic core member 16. During this same half-cycle of operation, current flows lfrom the supply terminal 66 through the load 56, the rectifier 68 in the forward direction, and the gate -winding 42, to the supply terminal 66, to thereby gate the magnetic core mem-ber 4W. The rectifier 64 during this half-cycle of operation prevents the flow of current through the gate Winding 42.

During the next Ihalf-cycle of operation when lthe supply terminal 32 is at a positive polarity with respect to the supply terminal 32 and the supply terminal 66 is at a positive polarity with respect to the supply terrninal 66', .current flows from the supply terminal 32 7 through lthe current-limiting resistor 60 and both branches of the parallel circuit 58, to the supply terminal 32', to thus gate the magnetic core member 16 land reset the magnetic core member 40". During this same half-cycle of operation control current flo-ws from the control terminal 62 through the current-limiting resistor 34, the reset windings 18 and 1S', to the control terminal `62 to thus effect a resetting of the magnetic core member 16. Simultaneously, current flows from the :supply terminal 66 through the gate winding 42, the rectifier 64 in the forward direction, and `the load 56, to the supply terminal 66', to thereby effect a gating of the magnetic core member 40. The rectifier 68 prevents the flow of current through the gate winding 4t2 during this latter half-cycle of operation.

The magnetic amplifier 54 of FIG. 3 has the same advantages as the magnetic amplifier 36 of FIG. 2 Iand in addition thereto provides half-cycle response in the second stage which includes the magnetic core members 40 and 40', since isolation is provided between the reset windings 38 and 38. Further, neither a forcing resistor (not shown) nor interstage filtering (not shown) is required between the two stages of the magnetic amplifier 54.

Referring to FIG. 4 there is illustrated `a half-wave magnetic amplifier 70 comprising two stages for effecting a halfewave voltage across a load 72 in accordance with a direct-current differential control voltage applied to control terminals 74 and 74 by a source 75. Like components of FIGS. 3 and 4 have been given the same reference characters. The main distinction between the :apparatus and circuits tof EIGS. 3 and 4 is that in the apparatus of FIG. 4 the parallel circuits 52 `and 58 have been so interconnected with the supply terminals 32 and 32 that the magnetic core members 16 and 16 are gated during the same half-cycle of operation and the magnetic core members 40 and Litl' are reset during this same halfcycle of operation. In addition, the load 72 is connected across the output diagonal of a Wheatstone bridge circuit 76.

The 'Wheatstone bridge circuit 76 includes two gate windings 78 and Sii which are `disposed in inductive relationship with the magnetic core member 46 and two gate windings 82 and S4 which are disposed in inductive relationship with the magnetic core member 49". Supply terminals 36 and 86', which 4are connected to a source 87 of alternating supply voltage which has suffi- Icient internal impedance to limit the flow of current through the gate windings '78, 80, 82 and 84 when both of the magnetic core members 4() and 40 are in the saturated state, are connected to .the input-diagonal of the Wheatstone `bridge 76. In practice, the alternating supply voltage applied to the supply terminals 86 and 86 is of the same frequency as the supply voltage applied to the supply terminals 32 and 32', and these supply voltages are so synchronized that when the supply terminal 32 is at a positive polarity with respect to the supply terminal 32, the supply terminal I86 is -at a positive polarity with respect to the supply terminal 86.

'As illustrated, the first leg of the Wheatstone bridge 76 includes ,the gate winding 8dv and a series connected rectifier 88; on the other hand, the second leg of the Wheatstone bridge 76 includes the gate winding 84 and a series connected rectifier 90 while the third leg of the bridge 76 includes the gate winding 78 and a series connected rectifier 92, and the fourth leg of the bridge 76 includes the gate Winding 82 Iand a seriesoconnected rectifier 94.

In order to effect a biasing of the magnetic core member 16 the reset winding 13 is connected in series circuit relationship with a rectifier 96 and with a biasing resistor 98, the series circuit being connected across the supply terminals 32 and 32. In like manner, in order to effect a like biasing of the magnetic core member 16', .the reset winding .18 is connected in series circuit 8. relationship with a rectifier 100 and with a biasing resistor 102, the later series circuit also being connected across the supply terminals 32 and 32. The rectiers 95 and 160 are so poled as to permit the ow of biasing current through the windings `18 and 18 only when the supply terminal 32 is at a positive polarity with respect to the supply terminal 32. 'For the purpose of resetting the magnetic core members `16 and 16 in accordance with the control voltage applied to the control terminals 74 and 74', the control terminals 74 and 74 are'interconnected, as shown in FIG. 4, with the reset windings 18 and 18. t

The operation of the magnetic amplifier 7) of FIG. 4 will now be described. Assuming the control terminal 74 is at a positive polarity with respect -to the control terminal 74 and assuming further that the supply terminal 32 is at a positive polarity with respect to the supply `terminal 32 and that the supply terminal 86 is at a positive polarity with respect to the supply terminal 86', then during this l1alfcycle of operation biasing current flows from the -supply terminal 32 through the biasing resistor 98, the rectifier 96 in the forward direction, and the reset winding 13, to the supply terminal 32', to thus bias the magnetic core member 16 a predetermined amount. Simultaneously biasing current flows from the supply terminal 32 through the biasing resistor 102, the rectifier iflfi in the forward direction, and the reset winding 1S', to the supply terminal 32', to thereby bias the magnetic core member 16' a like amount. During this same half-cycle of operation control current flows from the control terminal 74 through the rectifier 96, the reset windings 1S and 1S', and the rectifier ift-fi, -to the control terminal 74. The control `current flowing through the reset winding 18 under the assumed conditions is additive to the biasing current simultaneously flowing through the reset winding 18 and thus the additive effect of the control current sets the fiux level in the magnetic core member 16 still further away from positive saturation. However, the control current flowing through the reset winding 18 opposes the biasing current flowing through the reset winding 18 and therefore the magnetic core member 16' is set to a lesser flux level below positive saturation than is the magnetic core member 16.

During this same half-cycle of operation, when the supply terminal 86 is at a positive polarity with respect to the supply terminal 86', magnetizing .current flows from the supply terminal 86 through the four legs of the Wheatstone bridge 76. However, since the magnetic core member 49', during the previous half-cycle of operation, was reset to a lower level below positive saturation than was the magnetic core member 4f), the magnetic core member 45t saturates before the magnetic core member 4f), and therefore load current flows from the supply terminal 86 through the gate winding 82, the rectifier 94 in the forward direction, the load 72, the rectifier in the forward direction, and the gate winding 84, to the supply terminal 86. Finally, during this same halfcycle of operation, when the supply terminal 32 is at a positive polarity with respect to the supply terminal 32', the magnetic core member 4f) saturates and then current also fiows through the gate windings 78 and't) of the magnetic core member 4i), to thereby reduce the voltage across the load 72 to substantially zero value. Thus, current flows from right to left through the load 72, as shown, when the control terminal 74 is at a positive polarity with respect to control terminal 74 and the supply terminal 32 is at a positive polarity with respect to the supply terminal 32'. However, as hereinbefore xplained, this flow of load current through the load 72 occurs only between the time `that the magnetic core member 40' saturates and the time that the magnetic core member 411 saturates.

During the next half-cycle of operation, when the supply terminal 32 is at a positive polarity with respect to the supply terminal 32 and the supply terminal 86 is at a positive polarity with respect to the supply terminal 86, current flows from the supply terminal 32 through both branches of the parallel circuit 52 and the current-limiting resistor 30 to the supply terminal 32, to thereby effect a gating of the magnetic'core member 16 and a resetting of the magnetic core member 40 in accordance with the value to which the magnetic core mem- =ber 16 has been reset during the previous half-cycle. Simultaneously, current flows from the supply terminal 32 through both branches of the parallel circuit 58 and the current-limiting resistor 60, to the supply terminal 32, to thus effect a gating of the magnetic core member 16' and a resetting of the magnetic core member y40 in accordance with the flux level to which the magnetic core member 16 had been reset during the previous half-cycle of operation.

Assuming the polarity of the control voltage applied to the control terminal 74 and 74' reverses so that the control terminal 74 is at a positive polarity with respect to the control terminal 74, then during that half-cycle of operation when the supply terminal 32 is at a positive polarity with respect to the supply terminal 32', the control current flowing from the control terminal 74 through the reset winding 18 is additive to the biasing current owing therethrough while the control current flowing from the control terminal 74 through the reset winding 18 is subtractive from the biasing current flowing through the reset winding 13, and therefore the magnetic core member 16 under the latter assumed conditions, is reset to a flux level further below positive saturation than is the magnetic core member 16. Such being the case, during this half-cycle of operation when the supply terminal 86 is at a positive polarity with respect to the supply terminal 86', the magnetic core member 40 saturates before the magnetic core member 40 and during this interval between the saturation of the magnetic core members 40l and 40 load -current ows from the supply terminal 86 through the gate winding 80, the rectifier 88 in the forward direction, the load 72, the rectifier 92 in the forward direction, and the gate winding 78, to the supply terminal 86. Therefore, when the control terminal 74 is at a positive polarity with respect to the control terminal 74, load current lflows from left to right through the load 72, as shown.

During the neXt half-cycle of operation when the supply terminal 32 is at a positive polarity with respect to the supply terminal 32, current flows from the supply terminal 32 through both branches of the parallel circuit 52 and the current-limiting resistor 30, to the supply terminal 32, to thereby effect a gating of the magnetic core member 16 and a resetting of the magnetic core member 40 in accordance with the value to which the magnetic core member 16 has been reset during the previous half-cycle of operation. At the same time, current flows from the supply terminal 32 through both branches of the parallel circuit 58 and the current-limiting resistory 60, to the supply terminal 32, to thus effect a gating of the magnetic core member 16 and a resetting `of the magnetic core member 40 in accordance with the value to which the magnetic core member 16 had been reset during the previous half-cycle of operation.

The magnetic amplifier 70 of FIG. 4 also has the same advantages over the prior art as does the magnetic amplifier 36 of FIG. 2.

Referring to FIG. there is illustrated a full-wave magnetic amplifier 104 embodying further teachings of this invention in which positive feedback is provided for the magnetic amplifier. In operation, the magnetic amplifier 104 effects alternating voltage across `a load 106, the magnitude of which varies in accordance with the magnitude of a non-reversible -polarity direct-current control voltage applied to control terminals 108 and 108 by a source 109.

In general, the magnetic amplifier 104 comprises magnetic coreY members 110 and l112 which have disposed in inductive relationship therewith a reset winding r114, la feedback winding 116 and la tgate winding 124, and a reset winding 120, a feedback winding 122 and a gate winding 124, respectively, and supply terminals 126 and 126 Which 'are adapted to have connected thereto a source 127 of :alternating supply voltage. As illustrated, the load 106, which also functions as a current limiter, is connected in series circuit relationship with a parallel circuit 128, the series circuit being -connected across the supply terminals :126 and 126. One branch of the parallel circuit 128 includes the gate winding `118 and a rectifier 130 and the other branch of the parallel circuit 128 includes the lfeedback winding 122, a rectifier 132, and an adjustable resistor 134 which can be adjusted to vary the amount of feedback to the magnetic core member 112. The rectifiers 130 and 132 are so poled as to permit, only when the supply terminal 126 is 4at a positive polarity with respect to the supply terminal 126, the flow of current from the source 127 through both branches of the parallel circuit y128. In like manner, the load 106 is connected in series circuit relationship with respect to a parallel circuit 136, the series circuit being connected across the supply terminals 126 and 126. One branch of the parallel circuit 136 includes the gate winding 124 and a rectifier 138 and the other branch of the parallel circuit 136 includes the feedback winding 116, =a rectifier 140, and `an adjustable resistor 142 which can be adjusted to vary the amount of feedback to the magnetic core member 110. The rectitiers 138 and |140 are so poled as to permit, only when the supply termin-al 126 is :at a positive polarity with respect to the supply terminal 126', the flow of current from the source 127 through both branches of the parallel circuit v136.

In order to alternately reset the magnetic core mem- -bers 110 Iand 112 in accordance with the control voltage applied to the control terminals 108 and 108', the reset windings 114 and 120 are connected in series circuit relationship with a current-limiting resistor 144, the series circuit being connected across the control terminals 108 and 108.

The operation of the magnetic amplifier 104 of FIG. 5 will now be described. Assuming the supply terminal 126 is at a positive polarity with respect to the supply terminal 126, then current flows from the supply terminal 126 through both branches of the parallel circuit 128 land the load 106, to the supply terminal 126, to thus effect a gating of the magnetic core member 110 and a feedback to the ma-gnetic core member 112 until the magnetic core member 110 saturates. Thus, the amount of feedback to the magnetic core member L12 is in accordance With the 4amount that the magnetic core member 110 has been reset during the previous halfcycle of operation. During the same half-cycle of operation, when the supply terminal 126' is `at a positive polarity with respect to the supply terminal 126, current flows from the control terminal y108 through the currentlimiting resistor 144 and the reset windings 114 and 120, to thus effect ya 4resetting of the magnetic core member 112 during this half-cycle of operation in accordance with the magnitude of the control signal applied to the control terminals 108 and 108i. With the feedback winding 122 wound as shown, the current flow through the feedback winding 1122 effects a flux which is additive to the flux produced by the current flow through the reset winding 120, to thereby effect positive feedback. During this half-cycle of operation the rectifier 138 prevents a gating of the magnetic core member 112 and the rectifier 140 prevents a feedback to the magnetic core member 110.

During the next half-cycle of operation, when the supply terminal 126 is at ya positive polarity with respect to the `supply terminal 126, current flows from the supply terminal 126 through the load 106 'and both branches of the parallel circuit 136, to the supply terminal 126', to thereby effect a gating of the magnetic core member 112 and a feedback to the magnetic core member 11i) until the magnetic core member 112 saturates. At the same time, control current fiows from the control terminal itl-8 through the current-limiting resistor 114 and the reset windings i114 'and 120, to effect a resetting of the liux level in the magnetic core member 110 in accordance with the magnitude of the control voltage applied to the control terminals 108 and 108. With the feedback winding 116 wound as shown, the current flow through the feedback winding 11e effects a flux in the magnetic core member 110 that is additive to the flux produced by the control current owing through the reset winding 114, to thereby effect positive feedback. During this latter half-cycle of operation the rectifier 13) prevents :a gating of the magnetic core member 110 and the rectifier 132 prevents a feedback to the magnetic core member 112.

Referring to FIG. `6A there is shown la graph illustratin-g a transfer curve 150 yfor the magnetic amplifier 104,

of FIG. 5, when positive feedback is provided. It is to ybe noted that with no control signal input to the magnetic `amplifier 1M the output voltage of the magnetic amplifier can be at cut-off. In contrast, a transfer curve 152, in FlG. 6B, represents the; transfer curve for a conventional self-saturating magnetic amplifier (not shown) having positive feedback. Here it is to be noted that with no control signal input to this prior art magnetic amplifier (not shown) the output voltage of the magnetic amplifier (not shown) is at the satur-ating value.

Negative feedback for the :magnetic amplifier 104 can be provided by merely reversing the way in which the feedback windings die and 122 lare wound on their respective magnetic core members 110 and 112. A transfer curve 154, in FIG. 6A, represents the transfer curve for the magnetic amplifier of FIG. 5 when it is provided With'negative feedback. `It is to be noted that when negative feedback is provided for the magnetic amplifier of FIG. 5 and there is no control signal input, the output voltage of the magnetic amplifier can remain at the saturated value. In contrast a transfer curve 156, in FIG. 6B, represents the transfer curve for a conventional selfsaturating magnetic amplifier (not shown) when it is provided with negative feedback. Thus, in the case of the conventional self-saturating magnetic amplifier (not shown) with negative feedback, the output voltage cannot remain at the saturated value -with no signal input to the amplifier (not shown). In FIG. 6A a curve 153 represents the transfer curve for the magnetic |amplifier 104, of FIG. 5 when it is not provided with feedback. On the other hand, ia curve 166, 0f FIG. 6B, represents the transfer curve for a -conventional self-saturating magnetic amplifier (not shown) when it is not provided with feedback.

It is to be understood that three-legged magnetic core member (not shown) could be substituted for the magnetic core members 16 and 16 of FIG. 3. It is also to be understood that in the magnet-ic amplifiers shown in FIGS. 2 through 4 the two alternating supply voltages couldbe, and normally would be, obtained from a Voltage transformer (not shown) having two secondary windings. It is further to be understood that the reversible polarity direct-current control source 75, of FIG. 4, could be replaced by a reversibleaphase alternating control source (not shown) synchronized with and of the same frequency as the supply source 33. It is also to be understood that an alternating control source (not shown) could be substituted for the direct-current control source 13, of FIGS. l and 2, provided the polarity of the output of the alternating control source (not shown) is the same as that of the source 13 during the reset half-cycle of operation when the magnetic core member 16 is being reset.

Since numenous changes may be made in the above apparatus and circuits, and different embodiments may be made without departing from the spirit and scope thereof, it is intended that all matter contained in the foregoing description or shown in the accompanying drawingsrshall be interpreted as illustrative and not in a limiting sense.

I claim as my invention:

1. In a full-wave magnetic amplifier adapted to be connected to a source of alternating voltage to effect a voltage across a load, the combination comprising, magnetic core means, two gate windings and two feedback windings disposed in inductive relationship with the magnetic core means, circuit means for connecting said load and a first parallel circuit in series circuit relationship with respect to said source, one branch of said first parallel circuit including a first rectifier and one of the two gate windings and the other branch of said first parallel circuit including a second rectifier and one of the two feedback windings, other circuit means for connecting said load and a` second parallel circuit in series circuit relationship `with respect to said source, one branch of said second parallel circuit including a third rectifier and the other of the two gate windings and the other branch of said second parallel circuit including a fourth rectifier and the other of the two feedback windings, said four rectifiers being so poled as to permit, only during alternate half-cycles of the loutput of said source, the fiow of current from said source through said load and said first parallel circuit and as to permit, only during the other alternate half-cycles of the output of said source, thc flow Iof current from said source through said load and said second parallel circuit so as to effect an alternating voltage across said load, and means for resetting the flux level in said magnetic core means in accordance with a control signal.

2. `In a full-wave magnetic amplifier adapted to be connected to a source of alternating voltage to effect a voltage across a load, the combination comprising, a first magnetic core member having a gate winding and a` feedback winding disposed in inductive relationship therewith, a second magnetic core member having a gate winding and a feedback winding disposed in inductive relationship therewith, circuit means for connecting said load and a p first parallel circuit in series circuit relationship with respect to said source, one branch of said first parallel circuit including a first rectiher and the gate winding of the first magnetic core member and the other branch of said first parallel circuit including a second rectifier and the feedback winding of said second magnetic core member, other circuit means for connecting said load and a second parallel circuit in series circuit relationship with respect to said source, one branch of said second parallel circuit including a third rectifier and the gate winding of said second magnetic core member and the other branch of said second parallel circuit including a fourth rectifier and the feedback winding of said first magnetic core member, said four rectifiers being so poled as to permit, only during alternate half-cycles of the output of said source, the -fiow of current from said source through ,said load and said 'first parallelV circuit and as to permit, only during the other alternate half-cycles of the output of source, the flow of current from said source through said load and said second parallel circuit so as to effect an alternating voltage across'said load7 and :means for reset-V References Cited in the file of this patent UNITED STATES PATENTS 2,942,175 Wright June 2l, 1960 

1. IN A FULL-WAVE MAGNETIC AMPLIFIER ADAPTED TO BE CONNECTED TO A SOURCE OF ALTERNATING VOLTAGE TO EFFECT A VOLTAGE ACROSS A LOAD, THE COMBINATION COMPRISING, MAGNETIC CORE MEANS, TWO GATE WINDINGS AND TWO FEEDBACK WINDINGS DISPOSED IN INDUCTIVE RELATIONSHIP WITH THE MAGNETIC CORE MEANS, CIRCUIT MEANS FOR CONNECTING SAID LOAD AND A FIRST PARALLEL CIRCUIT IN SERIES CIRCUIT RELATIONSHIP WITH RESPECT TO SAID SOURCE, ONE BRANCH OF SAID FIRST PARALLEL CIRCUIT INCLUDING A FIRST RECTIFIER AND ONE OF THE TWO GATE WINDINGS AND THE OTHER BRANCH OF SAID FIRST PARALLEL CIRCUIT INCLUDING A SECOND RECTIFIER AND ONE OF THE TWO FEEDBACK WINDINGS, OTHER CIRCUIT MEANS FOR CONNECTING SAID LOAD AND A SECOND PARALLEL CIRCUIT IN SERIES CIRCUIT RELATIONSHIP WITH RESPECT TO SAID SOURCE, ONE BRANCH OF SAID SECOND PARALLEL CIRCUIT INCLUDING A THIRD RECTIFIER AND THE OTHER OF THE TWO GATE WINDINGS AND THE OTHER BRANCH OF SAID SECOND PARALLEL CIRCUIT INCLUDING A FOURTH RECTIFIER AND THE OTHER OF THE TWO FEEDBACK WINDINGS, SAID FOUR RECTIFIERS BEING SO POLED AS TO PERMIT, ONLY DURING ALTERNATE HALF-CYCLES OF THE OUT PUT OF SAID SOURCE, THE FLOW OF CURRENT FROM SAID SOURCE THROUGH SAID LOAD AND SAID FIRST PARALLEL CIRCUIT AND AS TO PERMIT, ONLY DURING THE OTHER ALTERNATE HALF-CYCLES OF THE OUTPUT OF SAID SOURCE, THE FLOW OF CURRENT FROM SAID SOURCE THROUGH SAID LOAD AND SAID SECOND PARALLEL CIRCUIT SO AS TO EFFECT AN ALTERNATING VOLTAGE ACROSS SAID LOAD, AND MEANS FOR RESETTING THE FLUX LEVEL IN SAID MAGNETIC CORE MEANS IN ACCORDANCE WITH A CONTROL SIGNAL. 